This proposal is to continue to develop, maintain, test, and evaluate the Image-Guided Surgical Toolkit (IGSTK). IGSTK is an open source software project that provides the basic components to develop an image-guided system. The initial version of the software was released to the public in February 2006 at the SPIE Medical Imaging Conference in San Diego and we continue to receive positive feedback from the user community. The software is currently available on the IGSTK web site for free download by any interested party under the BSD open source license. The software was developed under a Phase II STTR grant over the last two years, which will expire in August 2006. The ultimate goal of this project is to provide a robust, open source toolkit for rapidly developing image- guided software for research and clinical applications. To realize this goal, we need to continue to develop the toolkit and support the user community. Therefore, we are submitting this R01 proposal in response to the PAR-05-057 announcement "Continued Development and Maintenance of Software". The proposal is targeted at user support, software extensions, and the development of an FDA approved image-guided application and initial clinical trial. This is a three year project with four specific aims: 1. Support the IGSTK user community by responding to email requests, fixing bugs, developing documentation, and holding an annual users meeting at the SPIE Medical Imaging conference 2. Extend the existing software by developing: a. Multi-threading for better handling of multiple devices and heavy processing loads along with inter-process communication to simplify safe integration of IGSTK with other software packages b. Validation tools for the state machine model that the toolkit is based on 3. Develop an application template and programming guide to make it easier for new users to develop applications using the toolkit 4. Develop an image-guided application for lung biopsy incorporating electromagnetic tracking of the needle tip and pursue FDA/IRB approval for a pilot trial of 10 patients The completion of this project will provide an open source software system that will allow researchers to rapidly develop image-guided applications that will ultimately benefit patient care.